<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 300px;
            height: 300px;
            border: 1px solid #000;
            display: flex;
            align-items: end;
        }
        .inner{
            height: 100px;
            width: 100px;
            border: 1px solid #000;
            box-sizing: border-box;
            text-align: center;
            line-height: 100px;
        }
        .inner:nth-child(2){
            align-self: self-start;
            /* align-self: center; */
            /* align-self: self-end; */
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="inner">1</div>
        <div class="inner">2</div>
        <div class="inner">3</div>
    </div>
</body>
</html>